What this does

This document describes Lunar Lander's binary batch send endpoints, including streaming semantics and response behavior. The endpoint supports the following low latency transaction sending strategy:

• You send a binary body containing length-prefixed transactions
• The server starts parsing/sending transactions as bytes arrive (no need to wait for full body!)
• Response returns a summary (attempted, accepted, rejected, parse_error) instead of per-tx signatures

Endpoints

• POST /sendBatch

All batch endpoints require Content-Type: application/octet-stream.

Wire Format

The request body is a sequence of length-prefixed transactions:

• frame = u16_be_length + raw_tx_bytes
• u16_be_length is a 2-byte unsigned integer in big-endian order
• raw_tx_bytes is the serialized Solana transaction payload

Example with three transactions:

[len1_be][tx1][len2_be][tx2][len3_be][tx3]

Streaming Semantics

Batch bodies are decoded incrementally from the HTTP body stream:

• Each complete frame is parsed as soon as its bytes arrive
• Each parsed transaction is processed immediately (no wait for full body)
• Valid transactions before and after a rejected transaction are still attempted

Validation And Limits

• Maximum transactions per request: 16
• Minimum transaction payload size: 66 bytes
• Maximum transaction payload size: 1232 bytes

If framing breaks (for example, truncated length prefix/payload), already parsed prefix transactions are still attempted.

Response Contract

Response is always JSON:

{
  "attempted": 3,
  "accepted": 2,
  "rejected": 1,
  "parse_error": null
}

Fields:

• attempted: number of parsed transactions that were processed
• accepted: number of transactions accepted by ingress validation (includes deduped signatures)
• rejected: number of parsed transactions rejected by validation
• parse_error: framing/stream-level error object, or null

parse_error shape:

{
  "kind": "incomplete_payload",
  "at_tx_index": 3,
  "message": "incomplete transaction payload"
}

Notes:

• at_tx_index is 1-based
• for framing failures, at_tx_index points to the next frame being parsed

Status codes:

• 200 OK when rejected == 0 and parse_error == null
• 400 Bad Request when any parsed transaction is rejected or parse_error is present

Parse Error Kinds

• empty_body
• incomplete_length_prefix
• incomplete_payload
• max_batch_exceeded
• body_read_error
• rate_limited